Members of the PSL provide consulting services to scientists and physicians at NIH in different areas of applied mathematics and the physical sciences. A large segment of this effort is devoted to a study of the effects of head injury in veterans of Vietnam. We have continued our study of interpolation error in computerized tomography. We have examined experimental data and suggested further experiments with affinity chromatography to discover the causes of discrepancies from theoretical predictions. We have worked on combinatorial problems that arise from a method of fractionating DNA by alkaline elution.